Screw press with a delivery pipe and method for operating a screw press

ABSTRACT

A screw press features a feed pipe, in which a rotatable feed screw is arranged, and a feed cone, to which the feed screw conveys material, wherein drainage openings are arranged in the feed pipe. Drainage openings are preferably also provided in the feed pipe cone. Especially the combination of a feed screw with a feed pipe cone and a downstream compactor leads to a simple and effective compression of particularly liquid materials.

The invention pertains to a screw press with a feed pipe, in which a rotatable feed screw is arranged, and with a feed cone, to which the feed screw conveys material.

A screw press of this type is known, for example, from DE 200 00912 U1. This screw press serves for compacting and pushing waste material into a container. Dry waste materials can be initially pre-compacted in a conical pipe by means of this screw press and subsequently subjected to a final compaction by means of plates that can be moved toward one another. The screw press is designed for loose waste materials such as, for example, plastic bottles and serves for filling the container with compressed bottles as completely as possible.

The invention is based on the objective of treating wet waste materials such as pulp from a pulper with a screw press. These waste materials contain 5% to 20% solid matter and therefore 80% to 95% water in loose or bound form.

This objective is attained with a screw press of the initially cited type, in which drainage openings are arranged in the feed pipe cone and the feed screw ends at the transition from the feed pipe to the feed pipe cone.

It was unexpectedly determined that a screw press, which was designed for filling a container with compressed plastic bottles, can also be used for compacting pulp by simply arranging drainage openings in the feed pipe cone. The pressure of the feed screw makes it possible to press the material against the feed pipe cone and, in particular, to dewater the material at this location.

It was determined that it is particularly advantageous with respect to the function of the screw press if the feed screw ends at the transition from the feed pipe to the feed pipe cone. The screw therefore does not or only marginally extend into the feed pipe cone in order to achieve compaction therein. The friction in the primary compression zone is thereby significantly reduced because friction between the feed screw and the material to be compressed no longer occurs at this location. The compression is therefore realized by conveying the material into the cone. The screw does not extend into the cone in order to prevent the capillaries from being closed at this location.

The reduced friction leads to a reduced temperature increase. This is particularly relevant for materials that contain plastics. The temperature increase may cause the plastics to melt such that the material may fuse. If it is not only required to compress the material in order to minimize its volume, but a mechanical fractionation should subsequently also be carried out, the temperature increase during the dewatering process must be limited. The described screw press allows very significant dewatering without an excessive temperature increase. The control is adjusted in such a way that a temperature increase in fact occurs, but the molten plastics are prevented from fusing in order to promote the dewatering process.

If the waste materials are largely dewatered by means of presses without melting the plastics such as polyolefins, for example in the treatment of waste materials from the paper industry, the waste materials can subsequently be disagglomerated with simple means, for example, mechanically with screens and/or in an air separator.

It is particularly advantageous if the drainage openings are arranged in the radially inner region of the feed pipe cone. For this purpose, the surface of the cone is radially divided into two parts and the openings preferably are only arranged in the radially inner part of the surface.

It is particularly advantageous if drainage openings are arranged in the feed pipe. A screw press, which only features drainage openings in the feed pipe, also is a fundamental aspect of the invention because it is possible to forgo drainage openings in the feed pipe cone depending on the consistency of the material to be compacted.

The smallest diameter of the feed pipe cone has to be chosen in dependence on the material. It should be as small as possible in order to ensure a sound function of the cone, wherein the clear diameter of the cone must be chosen such that the materials to be compacted are not larger than the clearance of the cone.

It is advantageous if the drainage openings in the feed pipe cone are smaller in the region of the cone point than in the region of the cone base. In addition, more holes per surface area may be arranged in the region of the cone point than in the region of the base. The last row of holes and the holes with the smallest diameter are then decisive for the attainable maximum degree of drying. The holes in the region of the point may be realized in the form of oblong holes that preferably extend toward the point. The length of the paths to be traveled by the liquid through the conveyed material in the cone is thereby reduced. Fewer holes per surface area are preferably arranged in the region of the feed pipe in order to minimize the friction in this region.

In order to control or regulate the drive of the feed screw, it is proposed to arrange a pressure gauge in the feed pipe and/or in the feed pipe cone. However, this pressure gauge may also serve for controlling an addition of water on the feed pipe or in the feed cone in order to prevent high pressures, as well as to lubricate the screw press with water and thereby ensure continuous compaction.

Particularly the compaction of already pre-compacted material results in a temperature increase that indicates consolidation. It is therefore proposed to arrange a temperature measuring device in the feed pipe and/or in the feed pipe cone. The temperature measuring device also determines a value that can be used for controlling the feed screw drive and for controlling an addition of water to the screw press.

Since the screw press essentially serves for removing water from an aqueous material such as pulp, it is proposed to arrange a moisture measuring device in the feed pipe and/or in the feed pipe cone. In this way, control technology can ensure that dewatering is on the one hand achieved and excessive dewatering, which would impair the rotatability of the feed screw, is on the other hand prevented.

The dryer the pulp being conveyed, the higher the friction on the inner walls of the screw press. It is therefore proposed that the screw press has a polished and/or chrome-plated inner surface in certain areas. In this respect, it is advantageous if the inner surface of the feed pipe and/or the surface of the screw are at least in certain areas realized such that they generally little friction and preferably polished and/or chrome-plated. A polished and/or chrome-plated inner surface is also advantageous in the region of the feed pipe cone because high pressure between the material being conveyed and the inner side of the screw press is generated at this location.

Although the feed pipe of the screw press serves for dewatering materials, it is proposed that the feed pipe features a water inlet. A water inlet on the feed pipe makes it possible to maintain a liquid film on the inner surface of the feed pipe and to thereby promote the sliding motion of the material to be compacted toward the feed pipe cone. A corresponding water inlet may also be provided on the feed pipe cone, wherein this water inlet makes it possible to supply water to the screw press in certain operating states thereof in order to reduce the temperature and to improve the flow properties of the material being conveyed. The thusly generated hydraulic counterpressure can assist in improving the sliding properties of the material up to the cone in order to reduce the energy requirement.

A simple design of the screw press is achieved in that the feed screw has a constant diameter over its length. In this case, dewatering is primarily realized due to the counterpressure being generated in the feed pipe as a result of the narrowing at the feed pipe cone.

The feed screw makes it possible to achieve a certain degree of dewatering. More significant dewatering would lead to particularly high energy consumption of the screw. It is therefore proposed to arrange a compactor downstream of the feed pipe cone. This results in a two-stage compaction that allows a continuous flow of the material to be compacted.

When using a compactor of this type, it is advantageous if it features movable plates. This downstream compacting device consequently is based on a different compaction principle and thereby respectively allows particularly high compression and particularly sound dewatering. The compacting device used may consist of a device of the type known from DE 200 00 912 U1 and EP 1 118 455 A2. In the context of the present invention, we hereby refer to the full content disclosed in these publications.

In addition or as an alternative to a compactor with movable plates, it is furthermore proposed that the compactor features a rotatable compactor screw. This rotatable screw once again serves for conveying the material.

It is particularly advantageous if the compactor screw leads to a compactor cone. A compactor cone of this type serves as a resistance and makes it possible to further compact the material being conveyed.

A simple design is achieved in that the feed screw and the compactor screw are arranged on the same shaft. In this way, the feed screw and the compactor screw can be driven by the same motor or the same motors. It is proposed to arrange a gearing or a clutch between the feed screw and the compactor screw such that these two screws do not necessarily have to be driven with the same rotational speed. For example, a friction clutch between the feed screw and the compactor screw ensures that the feed screw does not stop at an excessively high resistance in the region of the compactor screw.

Depending on the material, the compactor, which is preferably driven with the same shaft as the feed screw, makes it possible to achieve any degree of dewatering from an agglomeration up to or nearly up to a fused mass with particularly high energy, cost and space efficiency.

If a shaft extending through the entire screw press is provided, it is particularly advantageous if the shaft, on which the feed screw and the compactor screw are arranged, is driven by motors on both sides. This reduces the risk of distorting the shaft when the material being conveyed generates particularly high resistances.

It is particularly advantageous if the screw press features an air separator that is arranged downstream of the feed pipe cone referred to the flow direction. This makes it possible to directly feed the dewatered material to the air separator after it exits the feed pipe cone or to treat the dewatered material mechanically with screening and/or vibrating devices prior to the air separation.

The above-defined objective of the invention is also attained with a method for operating such a screw press. The shaft of the screw press accordingly features a motor on one end and a generator on the other end, wherein the input power of the motor is reduced by the generator in order to control the shaft speed. This allows a simple control of the screw press.

In this context, it is advantageous if the generator is also used as a motor. It is particularly advantageous if the motors used on both sides of the shaft can also be used as generators. In this way, a power input or power output can be realized on the respective end of the shaft depending on the operating state of the screw press. The control may be based on the torques measured on the shaft.

It is also advantageous to measure the pressure, temperature and/or moisture of the material being conveyed on the inner side of the feed pipe and/or the feed pipe cone independently of the above-described steps.

These measured values may serve for controlling and regulating motors and generators. However, the measured values may also be used for controlling a water inlet for supplying water to the material being conveyed in order to simplify its flow through the screw press.

However, the measured values may also serve for adjusting the speed of the feed screw or the size of a clearance on the feed pipe cone and/or the compactor cone. If movable plates are used for compacting the material being conveyed, the position or the motion of the movable plates can also be controlled or regulated based on these measured values. Is therefore proposed to use the measured value for controlling the position of plates of a compactor.

The flow of the material being conveyed can be improved at any position of the screw press by adding water to the material. In regions that are provided with a water drainage opening, however, the flowability can also be improved by completely or partially closing the water drainage opening. It is therefore proposed to preferably also use the measured value for controlling water drainage from the material being conveyed.

Advantageous exemplary embodiments of screw presses are illustrated in the drawings and described in greater detail below.

In these drawings,

FIG. 1 shows a screw press with single-stage compaction and

FIG. 2 shows a screw press with two-stage compaction.

The screw press 1 illustrated in FIG. 1 essentially features a cylindrical feed pipe 2 and a rotatable feed screw 3 arranged therein. An inlet 5 is provided on an input end 4 and a funnel 7 is provided on an output end 6. The funnel 7 has an inner cone 8 formed by adjustable plates 9, 10 and an outer cone that serves as feed pipe cone 11 and is arranged downstream of the plates 9, 10 referred to the conveying direction. The feed pipe cone 11 features a water inlet 12, through which water can be supplied into the tapered region on the end of the cylindrical feed pipe 2 through openings 14 in the feed pipe cone 11 with the aid of a controlled valve 13.

In addition, the feed pipe cone 11 features a water drainage opening 14 with a controlled valve 15 in order to remove water from the tapered region 16.

The water inlet 12 may also serve, as a water drainage opening and the water drainage opening 14 may, in particular, also serve for the addition of water if the respective flow direction of the water is reversed.

Additional drainage openings 17, 18, 19 and 20 are located on the underside of the cylindrical feed pipe 2. The plates 9 and 10 may also feature openings or perforations in order to allow the throughput of water. These plates 9 and 10 are designed in such a way that their angular position relative to the cylindrical feed pipe can be adjusted in order to thereby realize an adjustable inner cone 8. If the inner cone 8 is adjusted particularly steep, the pressure of the material being conveyed increases in the region of the cylindrical feed pipe 12 such that the temperature of the material being conveyed may also increase. This is the reason why a temperature measuring device 21 is provided in the cylindrical feed pipe 2 and/or in the region of the inner or outer cone.

During the operation of the screw press, the material to be dewatered is introduced at the inlet 5, for example with 5% solid matter in the liquid medium, and conveyed along the cylindrical feed pipe 2. For this purpose, the feed screw 3 is turned with the aid of a (not-shown) motor. The material to be conveyed initially reaches the plates 9, 10 of the inner cone 8. This resistance results in dewatering of the material, as well as the drainage of water through the drainage openings 17-20. The material subsequently reaches the feed pipe cone 11, in which additional water is removed through the water drainage opening 14. The compressed material reaches the outlet 22, for example, with 90% dry mass.

If the temperature measuring device 21 determines an excessively high measured value, the plates 9, 10 of the inner cone 8 can be adjusted in order to reduce the counterpressure. In addition, the water drainage openings 17-20 can be closed and water may ultimately also be added through the water inlet 12 with the aid of the controllable valve 13 in order to prevent excessive compression and, in particular, fusing of the compressed material.

The special design makes it possible to maintain a certain residual moisture during the continuous operation of the screw press if the properties of the input material vary, namely without risking an undesirable physical material change due to excessively high pressures.

An enhancement of such a screw press is illustrated in FIG. 2. This screw press 30 features a feed pipe 31 and a rotatable feed screw 32. Drainage openings 33-37 are provided in the input region of the feed pipe 31 for dewatering purposes. Additional drainage openings 39, 40 are provided in the feed pipe cone 38. Pressure gauges 41 and 42, temperature measuring devices 43, 44 and moisture measuring devices 45, 46 are respectively arranged in the feed pipe 31 and in the feed pipe cone 38.

On the end that faces the feed pipe cone 38, the feed pipe 31 has in its cylindrical region a polished inner surface 47 that is connected to a water inlet 48 in order to produce a liquid film 49 on the inner side of the feed pipe 31.

A compactor 50 featuring movable plates 51-53 is arranged downstream of the feed pipe cone 38. The compactor 50 essentially features a cylindrical pipe 54 with movable plates 51-53 and a rotatable compactor screw 55. This compactor screw 55 conveys the already compacted material to a compactor cone 56 in order to additionally compress the already compacted material. The compactor also features a water drainage opening 57 that can preferably be closed in order to control the water drainage in the region of the compactor. A water inlet 58 is provided in order to prevent excessively high temperatures. The virtually dry compacted material ultimately exits the compactor through the outlet 59.

The feed screw 32 and the compactor screw 55 are arranged on the same shaft 60 and the shaft 60 is driven on its ends by motors 61 and 62. Both motors may also serve as generators.

During the operation of such a screw press, for example, the shaft 60 is slowly turned by means of the two motors 61 and 62. If the plates 51-53 are steeply adjusted, the clearance in the region of the plates is reduced such that significant counterpressure is generated. This leads to a high temperature in the region of the compactor 50. If the temperature reaches excessively high values, the angles of the plates 51-53 can be reduced such that the clearance is enlarged. This causes a decrease in the resistance such that the material is conveyed faster through the screw press by the motor 61 and 62. The temperature in the region of the compactor 51 thereby decreases accordingly.

Particularly the option of also using the motors as generators makes it possible to achieve continuous compaction with simple motors and little control effort.

In an exemplary embodiment, beverage cartons are pre-treated in a pulper or a processor of the type described in WO 2013/135224, to the full content of which we hereby refer, wherein the residual materials are, if applicable, concentrated in a hydro-cyclone. Subsequently, the residual materials are dewatered in the screw press and PE-HD and PE-LD are then separated in an air separator. In this context, it must be strictly observed that the plastics do not melt in the screw press because molten or fused plastic fractions are unsuitable for air separation. 

1. A screw press (1, 30) with a feed pipe (2, 31), in which a rotatable feed screw (3) is arranged, and with a feed pipe cone (11, 38), to which the feed screw (3, 32) conveys material, wherein drainage openings (39, 40) are arranged in the feed pipe cone (11, 38) and the feed screw (3, 32) ends at the transition from the feed pipe (2, 31) to the feed pipe cone (11, 38).
 2. The screw press according to claim 1, wherein drainage openings (17 to 20, 33 to 37) are arranged in the feed pipe (2, 31).
 3. The screw press according to claim 1, wherein the drainage openings in the feed pipe cone are smaller in the region of the cone point than in the region of the cone base.
 4. The screw press according to claim 1, wherein more holes per surface area are arranged in the region of the cone point than in the region of the cone base.
 5. The screw press according to claim 1, wherein a pressure gauge (41, 42) is arranged in the feed pipe (2, 31) and/or in the feed pipe cone (11, 38).
 6. The screw press according to claim 1, wherein a temperature measuring device (21, 43, 44) is arranged in the feed pipe (2, 31) and/or in the feed pipe cone (11, 38).
 7. The screw press according to wherein a moisture measuring device (45, 46) is arranged in the feed pipe (2, 31) and/or in the feed pipe cone (11, 38).
 8. The screw press according to claim 1, wherein it has a polished and/or chrome-plated inner surface (47) at least in certain areas.
 9. The screw press according to claim 1, wherein the feed pipe (2, 31) features a water inlet (48).
 10. The screw press according to claim 1, wherein the feed screw (3, 32) has a constant diameter over its length.
 11. The screw press according to claim 1, wherein a compactor (50) is arranged downstream of the feed pipe cone (11, 38).
 12. The screw press according to claim 11, wherein the compactor (50) features movable plates (51 to 53).
 13. The screw press according to claim 11, wherein the compactor (50) features a rotatable compactor screw (55).
 14. The screw press according to claim 13, wherein the compactor screw (55) conveys material to a compactor cone (56).
 15. The screw press according to claim 13, wherein the feed screw (3, 32) and the compactor screw (55) are arranged on the same shaft (60).
 16. The screw press according to claim 15, wherein the shaft (60) is driven by motors (61, 62) on both sides.
 17. The screw press according to claim 1, wherein it features an air separator that is arranged downstream of the feed pipe cone (11, 38) referred to the flow direction.
 18. A method for operating a screw press (30) according to claim 1, wherein the shaft (60) of the screw press (30) features a motor (61) on one end and a generator on the other end, and in that the input power of the motor (61) is reduced by the generator in order to control the shaft speed.
 19. The method according to claim 18, wherein the generator is also used as a motor (62).
 20. The method according to claim 1, wherein the pressure, temperature and/or moisture of the material being conveyed is measured on the inner side of the feed pipe (2, 31) and/or the feed pipe cone (11, 38).
 21. The method according to claim 20, wherein the measured value is used for controlling a water inlet (12) for supplying water to the material being conveyed.
 22. The method according to claim 20, wherein the measured value is used for controlling the speed of the feed screw or for adjusting a clearance of the feed pipe cone (11), the compactor cone or movable plates (7, 34).
 23. The method according to claim 20, wherein the measured value is used for controlling the position of plates of a compactor.
 24. The method according to claim 1, wherein the measured value is used for controlling water drainage from the material being conveyed. 